Microphysical properties of ice and mixed-phase cloud particles as revealed by GPM microwave polarimetric measurements and radiative transfer modeling

GALLIGANI, VICTORIA; D. WANG; PRIGENT, CATHERINE; SALIO, PAOLA

Conferencia; American Geophysical Union (AGU) Fall Meeting; 2019

Retrieving information about the microphysical properties of frozen and mixed phase clouds (particle size, shape, density, ice water content) is key to improve our understanding of cloud microphysical processes and their representation in weather prediction models, yet remains a challenging aspect in space-based precipitation observations. Passive microwave radiometry has shown a promising ability in the characterization of frozen particles, as it is able to penetrate into clouds and provide unique insight on their internal structures. Microwave cloud polarized signals have additionally shown information on frozen particle shapes (aspect ratio) and orientation. The launch of the GPM Microwave Imager (GMI) has extended the availability of microwave polarized observations to higher frequencies (166 GHz), previously only available up to 89 GHz. Cloud polarized signals provide information on stratiform clouds resulting from the highly polarized scattering caused by the horizontal orientation of non-spherical frozen habits. This study analyses one-year of GMI observations. Stratiform clouds show larger polarized signals (~10K) due to the deposition and aggregation growth of snowflakes, while the convective regions show smaller polarization, as graupel and/or hail become randomly oriented due to collision/break-up processes in strong updrafts. A robust relationship has been found between the polarization difference and the vertical polarized brightness temperature over both land and ocean surfaces, and is parameterized using Hermite cubic spline interpolation. The regional and seasonal variability is also investigated between different cloud regimes. A radiative transfer (RT) modeling framework is applied for deep convection cases in Southeastern South America which physically support the statistical relationships parameterized. Two different scattering solvers within the Atmospheric Radiative Transfer Simulator (ARTS) are coupled with the Weather and Research Forecasting (WRF) model to explore the sensitivity of polarized signals to ice particle microphysics parameters (aspect ratio, orientation, density). Both coincident GMI observations and ground radar polarimetric measurements are exploited to evaluate the RT simulations.